There is a superconducting coil assembly which is formed by, for example, winding a tape-shaped superconducting member that is bismuth-based, yttrium-based, or such like, around a bobbin to form a coil unit in a shape such as a pancake, a fan, or a racetrack, and then arranging a plurality of these coil units coaxial to the same direction.
In such a superconducting coil assembly, the magnitude of critical current of the superconducting member is known to depend on the strength of the magnetic field acting on the superconducting member. More specifically, the magnitude of critical current of the superconducting member mainly depends on the strength of the magnetic field acting in a direction that is perpendicular to a wide surface of the superconducting wire tape (i.e. the diameter direction of the coil unit), and the magnitude of critical current decreases as the strength of the magnetic field in the perpendicular direction increases. Also, in a superconducting coil assembly for AC current, there is a problem of loss (AC loss) due to an alternating magnetic field, which is a characteristic of superconductivity.
To counter this problem, Patent Document 1 discloses a member wherein magnetic field adjusting members, made by dispersing iron powder composed of a ferromagnetic material such as pure iron in resin, are arranged via electrical insulating members between coil units that are adjacent in the axial direction. According to this structure, magnetic flux penetrating the superconducting material is captured by the magnetic field adjusting members, thereby the strength of the magnetic field acting on the superconducting material in the diameter direction is reduced and a reduction in critical current is suppressed.
[Prior Art Documents]
[Patent Documents]
[Patent Document 1] Japanese Patent Publication No. 2004-342972